1. Field of the Invention
The present invention relates to an image reading device which, while a film on which a plurality of frame images have been recorded is being conveyed, reads light transmitted through or reflected by the frame images so as to obtain image data.
2. Description of the Related Art
Technology for forming images onto recording materials as follows has come to be known in recent years. Frame images recorded on an original such as a film are photoelectrically read by a reading sensor such as a CCD. Image processing such as enlargement/reduction and various types of correction is then carried out on digital image data obtained by this reading. Images are then formed at recording materials by laser light modulated on the basis of the image-processed digital image data.
In this technology for digitally reading frame images by a reading sensor such as a CCD, in order for image reading to be performed accurately, the frame images are read preliminarily (which is known as prescanning), reading conditions (e.g., quantities of light to be illuminated onto the frame images, charge accumulation times of the CCD and the like) corresponding to density and the like of the frame images are thereby determined, and the frame images are read again under the determined reading conditions (which is known as fine-scanning).
Prescanning and fine-scanning are carried out by one optical system. Namely, first, in prescanning, light emitted from a halogen lamp is transmitted through the conveyed film, this transmitted light is detected by the CCD sensor, and the frame images on the film are thereby read. Then, based on results of prescanning for each frame image, the reading conditions for fine-scanning are respectively set for each frame image.
After the reading conditions for fine-scanning have been set for all of the frame images, the film is conveyed in a direction opposite to a direction in which the film was conveyed during prescanning, and fine-scanning is carried out for each frame image.
In fine-scanning, because the film is conveyed in the direction opposite to the direction in which it was conveyed during prescanning, fine-scanning is carried out sequentially from a last frame to a first frame. A conveying speed for fine-scanning is set at a speed slower than for prescanning, and reading resolution thereby increases correspondingly.
However, in the above-described method, all of the frame images on the film are prescanned and then the film is conveyed in the opposite direction and all of the frame images are fine-scanned. Therefore, a large amount of time is needed from the start of prescanning to the end of fine-scanning.